Artificial network



July 1937- w. CAUER ET AL 2,085,952

I ARTIFICIAL NETWORK Filed Dec. 29, 1935 1 2 Sheets-Sheet 1 July 6, 1937. w. CAUER ET AL 2,085,952

ARTIFICIAL NETWORK Filed Dec. 29, 1953 2 Sheefs-Sheet 2 Patented July 6, 1937 ARTIFICIAL NETWQRK Wilhelm Cauer and Ernst Glowatzki, Gottingen, Germany Application December 29, 1933, Serial No. 704,460

- In Germany January 23, 1933 3 Claims. (01. 178-44) The present invention relates to electrical-imare of about the same value as the other circuit pedance or artificial networks, such as are used elements of the network. In special cases, where for attaining or approximating to predetermined the coupling is tight, the windings may be wound frequency characteristics. bifilar. In some special cases, where the loading Anetwork having impedance that approximates impedance shunts both the windings, the gen-' to the frequency characteristics of a telephone eral idea of the invention leads to a network of line or a combination of telephone lines, for exthe known bridged-T type. ample, is an impedance or artificial network. An The reason for the various conditions set out attenuation or phase-distortion-correction netin the foregoing paragraph and the rules how to Work is also an impedance or artificial network pp y t e i ve ti to a given prehlemwill 10 because it produces the desired attenuation or come clear after a discussion of several examples.

phase correction as a function of frequency. It can be mathematically demonstrated and Wave filters and retarding networks are further will be illustrated hereinafter-in connection with such examples. Figs. 4 to 6 that, especially for each symmetrical- An object of the present invention is to provide ea t four-terminal w a tw r 15 new and improved impedance or artificial net- Without superfluous circuit elements may be obworks. I tained by applying mutual inductance, according In Siebschaltungen, v. D. I. Verlag, 1931, Wilto the invention, a but a single place, and this helm Cauer, there is disclosed, in Fig. 4, for ex- Constitutes another object of the present invenample, an artificial network having comparatively tiOIl- The resulting e my Of O tru0ti0n Of' 0 many ordinary transformers, constituting the artificial networks is obvious. The invention is equivalent of a symmetrical, f ur-ter i l tnot, however restricted to artificial networks of work without mutual inductances, but that is this Character, d is p l e o t e 'fourmore economical than the latter symmetrical netterminal etw r s.

work in that it contains fewer circuit elements. In the accompanying drawings, Figs- 1 '0 are Another object of the invention is to reduce the diagrammatic ws us a n a tific al n tnumber of such transformers in artificial net- Works embodying the n O FigS- 4 t0 6 are works. similar views of wave filters, constructed in ac- The employment of practically i l crane cordance with the present invention; and Figs. 7

formers is often di advanta e and further and 8 are similar views illustrating the invention 30 object of this invention, therefore, is to avoid such as applied o Separating fi suse. In all the figures of the drawings, a pair of in- The present invention further contemplates a put terminals of the network Shown at I,

new and advantageous application of mutual inand a pair o O p termihalset n s.

ductance in artificial networks. Tothis end, a and an additional P f tp t er nals 35' feature of the invention resides in having the an is indicated at n, n','and there may be as many tificial network comprise two pairs of terminals additional pairs of output terminals as desired. and, besides other circuits, one mesh going The input terminals may, of course, be employed through one pair of the terminals and another as the output terminals of the network, in which 40 es going through the Other p of terminals, case the output terminals shown would be used as 40 the two meshes having a common branch, and the input terminals. each containing further an additional branch that Two-terminal impedances, each having at least is not common, but that COmDriS S wi d n s 00 two circuit elements, are shown at a. These twopled to constitute a transformer, the transformterminal impedances are assumed to have a value er being loaded by an impedance containing at different from zero at zero frequency, even ifre least two circuit elements. Such impedance is sistances are neglected, but they are not restrictcalled lumped impedance. The transformer may ed in character, except to this extent.

be loaded by direct galvanical connection or by The impedances of the two-terminal networks tight or loose coupling by a special winding. The indicated at b have no restrictions whatever. 50 loading impedance should be such that it is difn a the figu except Fig. t e i ow ferent from zero at frequency zero, even if rea star of capacities, such as the capacities ll, l2 sistances are neglected. The loading impedance, and IS in Fig. 1. These are necessary in order furthermore, should not lie in either of the said that the networks may be suitable, without exceptwo meshes, The inductances of the windings tion, for use as symmetrical wave filters In special cases, of which the network illustrated in Fig. 4 is an example, these capacities become infinite.

Of the two before-mentioned meshes, referring first to Fig. 1, one extends from terminal I, through a coil I4, the two-terminal network b and the capacities l3 and H, to the terminal I. The other mesh extends from terminal 2, through a coil IS, the two-terminal network b and the capacities l3 and |2, to the terminal 2'. The common branch thus contains the two-terminal network b and the capacity I3. The branches that are not common contain the coils l4 and I5, which are of finite inductance, but which are coupled inductively to form a transformer. This transformer is loaded by coupling the coils l4 and IE to a winding l6, and closing the winding l6 through the two-terminal network a. The impedance network a is thus formed of at least two circuit elements and is infinite for direct current and does not belong to one of the two meshes.

7 In Fig. 2, one of the meshes [extends from the terminal I, through a coil 28, the two-terminal network b and the capacities l9 and H, to the terminal I. The other mesh extends from the terminal 2, through the coil 2 I, the two-terminal network b and the capacities l9 and I8, to the terminal 2'. The common branch contains the two-terminal network b and the capacity I 9. The branches that are not common contain the coils 28 and 2|, of finite inductance, but coupled inductively to form a transformer. This transformer is loaded by connecting the two-terminal network galvanically with the ends of the winding 20, in the manner of an autotransformer.

Fig. 3 represents a balanced form of the network of Fig. 1. The common branch of both the meshes contains the two-terminal network I) and the capacity 3|. One mesh extends from the terminal I, through a condenser 23, a coil 30, this common branch 1), 3|, a coil 26 and a condenser 22, to the terminal I. The other mesh extends from the terminal 2, through a condenser 25, a coil 29, the common branch b, 3|, a coil 21 and a condenser 24, to the terminal 2. The inductively coupled branches that are not common may be assumed, according to the invention, to be those with the coils 26 and 21 or those which the coils 29 and 30. The transformer formed by the coils is in each case loaded by the two-terminal network a by connecting it in circuit with a winding 28 that is coupled to the coils. The condensers 22 and 23 and the condensers 24 and 25 have, in pairs, equal values of capacity.

In Fig. 4, there is illustrated a symmetrical wave-filter of the Cauer class 3b (see Cauer, New Theory and Design of Wave Filters, Physics, vol. 2, No. 4, 1932, pages 242 to 268, and other Cauer publications there cited, but embodying the invention according to Fig. 2. The coils 38 and 39 form a transformer, as described in connection with the coils 20 and 2| of Fig. 2. These coils have the same, essentially finite inductance, and are tightly coupled. Such a transformer may be constituted, in practice, for example, by a double-wound transformer with a closed iron core. This transformer is shown loaded by a two-terminal network a formed by two condensers 35 and 36 in parallel to each other and to the coil 38, and one coil 31 in series with the condenser 38. The common branch of the meshes comprises a coil 32. and 34 con ens 33 in series, with a coil 40 and a condenser 34 in shunt thereto and to each other. At zero frequency, the two-terminal network a has infinite impedance. The advantage of this invention is shown by a comparison thereof with a known, equivalent network, without superfluous elements, containing two non-ideal transformers, such as is shown in Fig. 13 of the before-mentioned Siebschaltungen.

Reference has been made above to a Cauer class 31). Though this nomenclature is now understood by persons skilled in the art, it may be stated, for greater clearness, that a filter belongs to this class 311-, if it is equivalent to a lattice section (see, for example, Fig. 1 of the Siebschaltungen or Cauers said article in Physics, Fig. 3) Where the two-terminal networks opposite to each other are equal in pairs and have the impedance functions where wl and -1 are the cut-off frequencies, m, w, and w are'p-arameters and )\=iw, where w is the pulsatance.

In Fig. 5, the invention is shown applied, according to Fig. 2, to a symmetrical wave-filter of the Cauer class 311*. The transformer is formed by the tightly coupled coils 48 and 49 that, like the coils 20 and 2| of Fig. 2, and 38 and 39 of Fig. 3, have the same, essentially finite inductance. This transformer is loaded by a two-terminal network a, formed by a seriesconnected condenser 46 and coil 4'! connected across the coil 48. The impedance b, in this case, is shown as a coil 50, shunted by a series connected coil 44 and condenser 45. A zero frequency, the two-terminal network a has infinite impedance. This figure especially shows the advantage of the invention; for filters of class 311* have heretofore been constructed by W. Cauer (see Siebschaltungen, Figs. and 11) by means of two and four transformers.

The examples above deal with symmetrical, four-terminal networks. Rules will now be given for applying the invention to symmetrical quadripoles.

A network of lattice type, equivalent to any such network for all frequencies, can be designed, as is known in the art-see, for example, the above-mentioned article in Physics. Using the same notation as in the said article, one pair of equal, opposite, lumped impedances of the lattice may have the value Z1, the other pair the value Z2. The further discussion will be restricted to the case where the symmetrical quadripole is composed of reactances and, therefore, Z1 and Z2 are reactance functions. The above example of a filter of class 3b is a special case of the nature of the reactance functions Z1 and Z2. More generally, it is shown in the Siebschaltungen .how to design the functions and impedances Z1 and Z2 to obtain a filter with prescribed characteristics. By known theorems, a given reactance function Z1 or Z2 can be realized by different structures (R. M. Foster, A Reactance Theorem, Bell Syst. Techn. Journ., vol. III, No. 2, April 1924, and W. Cauer, Die Verwirklichung von Wechselstromwiderstanden vorgeschriebener Frequenzabhangigkeit, Archiv f. Elektrotechnik,

actance function where Z1 is the above function for class 3b, is realized by a structure shown in Fig. 4 containing the coils 32 and 40 and the capacities 33 and 34. Similarly, in the case of class 31),

is realized by the structure containing the, coils 3! and 3B and the capacities 35 and :36.- .In general, any lattice with lumped impedanc'es (reactances) Z1 and Z2 can be replaced'byj the equivalent quadripole of structure Fig. 2, where the impedance structures for Z1 and Z only appear once instead of twice in the lattice. If at least one of the Z1 and Z2, say Z1, is zero for direct currents, the capacities l1, l8 and I9 are infinite (or capacity l9 may be included in the impedance b, as the case may b'e), and

T is realized by a structure a shunted-by the coil 20 and is realized by a structure b. If coil 2| is then made equal to coil 26, and both are coupled tightly, the network of Fig. 2 is equivalent to the lattice with pairs of impedances Z1 and Z2. If, however, Z1 and Z2 are not zero for direct currents, acapacity of impedance value can be separated from Z1 and another capacity of impedance value can be separated from Z2 so that the remaining part of is zero for direct currents and can be realized as before. If necessary, an interchange of Z1 and Zz,which does not affect the characteristics of the quadripole except a phase change of 1r radians,-takes care of the condition of physical realizability that D1920. As well as capacities, inductances might be separated from and before realizing the rest as before. This is shown by the example of a filter of class 3d, which is shown in Fig. 6.

In Fig. 6, there is shown, according to the invention, for carrier telephony, a filter network of the Cauer class 3d, with loose coupling between the coils 62 and 63. These coils 62 and 63 and a coil 6| are connected between the terminals and 2. The condensers 58 and 59 and coil 66 are connected like the condensers 35 and 36 and the coil 3! of Fig. 4. The impedance 1:

is. constituted' of coils 55, 51 and 64 in series, the coils 55 and '51--:being respectively shunted by condensers andi56." L'The condensers 5|, 52 and .53i-are'c0nnected like the condensers II, l2, l3 of-Fig. 1. -J 1 [The said separated .coils are 6|, 64' and a coil of the same value as coil 6|, which is joined with coil 2|in. the notationof Fig. 2, and is part of the coil 63. i It follows. that the coils 62 and 63. are coupled loosely, which might be annadvantagein the case of :higherfrequencies. The separating ofga. coil 6| .from -Z1 has thefurther advantage that the remaining impedance (namely, the-.elementsf-58, 59,. 66s, and 62), between the terminali at the junction of the elements .6 and 62, and the terminal atv the-junctionof the ele-'- ments 58 and 64 is zero at infinite frequency and, therefore, contains -a "capacity 158. in parallel, which might beadjustedto compensate theundesired inter-winding.capacity'ofthe"coil 62.

- .In Figs. 7 and 8.,ithe:inventiondsshown applied to separatingzfilters such, for example,-as areused for. carrieritelegraphyz In Fig. '7, it "is assumed that there-are n+1 filters withdifferent pass-bandseach ;constructed-:as in Fig. 2,:.=an'd shuntedtwith oneside66 ofjthe transformer 65, 66. The coil 65,0f the transformer is connected between .the;terminals.:|, l, with theopen-air wire or-the cabled Here the network becomes balanced by: earthingrof the middle. of vthecoil 65.; At: the receive'r end;ia similar'networkwill be'used; sIf,atthe terminalsz, 2'2 n,-n', n-'-1 carrier telegrams are"sent,'they {may be heard at the receiver end "at the corespondingif terminals of the receiving netwdf 1 v The same 'eifectmay be' obtained with the 11- 1 several filters of'Fig."*2 connected in series, as illustrated in Fig. 8. connected like the coils 65 and 66 of Fig. 7. The Fig. 2 filters are not assumed to have any special position. The several filters may be designed as well according to Fig. 1, or to Fig. 3.

In particular, the partial filters of the separating filter of Fig. 7 may be chosen according to Fig. 5, as a filter of the class- 311*; or, in Fig. 8, the partial filters may be chosen asfilters of class 3b, according to Fig. 4'.

Although the couplings of Figs. 4 and 5 were described as tight, it may be useful, in connection withcarrier telephony, for example, to use mutual inductances, according to this invention, in the form of loose couplings, with coils without iron, as before described in connection with Fig. 6.

It is obviously impossible to describe in detail all the special applications of the present invention. They will be understood by persons skilled in the art without further description. 'It is therefore desired that the appended claims be broadly construed, unlimited except insofar as limitations may be necessary to be imposed by the state of the prior art. 7

What is claimed is:

1. A separating filter having two input terminals and a plurality of pairs of output terminals and comprising two or more four-terminal networks connected with the input terminals, each network attaining or approximating to prescribed frequency characteristics, but the different networks being designed to pass different The coils 61 and 68 are bands of frequencies, at least one of the fourwith the corresponding input terminals and the output terminals, the two meshes having a common branch,-each mesh having a branchthat is not common and thatis provided-with a winding, the windings being coupled together to constitute a transformer, the inductances of the windings being of about the same value as the other circuit elements of the network, the primary winding of the transformer being shunted by a loading'reactance that is of infinite value for direct currents, the secondary winding of the transformer and the windings as a unit not being shunted, and the different networks being designed to coact to produce an. efficient separating filter, notwithstanding that some or all of the said difierent networks areindividually not ef ficient filters.

- 2. A separating filter comprising a connection in series of two or more filters of "the Cauer class 3b, each filter comprising a four-terminal, electrical-impedance network attaining or approximating to prescribed frequency characteristics,'but' the different networks being designed to pass diiferent bands of frequencies, each network having 'a pair of input terminals and a pair of output terminals and being provided with two meshes'respectively connected with the in put terminals and the output terminals, the two meshes having a common branch, each mesh having a branch that is not common and that is provided with 'awinding, the windings "being coupled together to constitute a transformer, the inductances of the windings being of about the same value as the othereircuit elements of the network, the primary winding; of the transformer being shunted by a loading lumped impedance that is of infinite value for direct currents, the

secondary winding of the transformer and the windings as a unit not being shunted, the elements of the different networks having different values, and the different networks being designed to coact to produce an efficient separating filter, notwithstanding that some or all of meshes having a common branch, each mesh havinga branch that is not common and that is provided with a winding, the windings being coupledtogether to constitute a transformer, the inductances of the windings being of about the same value as the other circuit elements of the network, ,the. primary winding of the transformer being shunted by a loading lumped impedance that is of infinite value for direct currents, the secondary winding of the transformer and the windings as a unit not being shunted, the elements of the different networks having different values, and the different networks being designed. to coact to produce-an efficient separating filter, notwithstanding that some or all of the said networks are individually not efficient filters. I

WILHELM CAUER.

ERNST GLOWATZKI. 

